The invention relates to a method and a device for machining robot-guided components, in particular turbine blades.
A method is known from European Patent Document No. EP 2 014 413 A1. In this case, a robot guides individual compressor blades to one or multiple grinding machines in order to restore an optimized leading edge contour. A sensor on a grinding disk detects a contact pressure that the robot-guided blades exert on the grinding disk. This force measured value is able to be taken into consideration in the movement process of the robot in order to compensate for component tolerances. EP 2 014 413 A1 does not disclose how the measured value in the movement process is taken into consideration.
The object of the present invention is improving the machining of robot-guided components.
The present invention may be used in particular for machining turbine blades, for example guide blades or rotor blades of compressors, compressor stage(s) or turbine (stages) of aircraft engines, wherein preferably a plurality of blades connected to one another, for example integrally bladed rotors (blisk), a complete guide vane assembly or rotor assembly or a portion of such an assembly may be handled by a robot. The machining may take place in particular during the new manufacture or a repair of the blade(s).
According to the invention, a component, for example a blade, is guided by at least one robot to at least one tool which machines the component in the process. Components may also be advantageously guided by the same robot or, in particular selectively, for instance depending upon the component and/or tool, by different robots to the same tool, selectively to, for example differently configured tools or tools replacing one another and/or in succession to different tools. Tools machine the component preferably in a rotating manner and/or under the application of a specific contact force, for instance in a metal-cutting manner, by grinding, polishing or the like.
For example, a robot may pick up rotor blades or a rotor blade disk (blisk) and guide them to a grinding station on a grinding disk. Then the same or another robot may guide the same component to a polishing station on a polishing disk. In the meantime, a further robot may already guide another blade (disk) to the grinding disk so that the grinding disk is utilized in an optimal manner and the throughput is increased. Similarly, heavier blades or blade disks, for example, may be guided by more powerful robots to the same tool. In addition a plurality of the same kind of machining stations may also be provided in order to substitute for one another, for instance during replacement of a grinding disk or the like, so that the robot(s) are better utilized.
One or a plurality of the tools is fastened in an articulated manner to the same or different, moveable or stationary tool holders. In a preferred embodiment, a tool in this case has at least one, in particular at least two and preferably three or more degrees of freedom, in particular rotational degrees of freedom, the coordinates of which are detected for detecting a deflection of the tools fastened in an articulated manner with respect to the tool holder.
A rotational degree of freedom is preferably realized by a pivot joint with an axis. Two or more rotational degrees of freedom may be realized by a pivot joint with the corresponding number of axes, for instance ball joints or Cardan joints, or, preferably, by one or multiple coupling elements, wherein then the tool or a tool receptacle is fastened by a, preferably single-axis, pivot joint to a coupling element, for example an extension arm, and the coupling element for its part by an, again preferably single-axis, pivot joint to the tool carrier or a further coupling element, which for its part is then fastened to the tool carrier, if need be with the interconnection of additional coupling elements and pivot joints. Translational joints, for instance rail guides or the like may be provided instead of some or all of the pivot joints. Two or more axes of the articulated fastening, in particular axes of rotation of pivot joints, are preferably parallel to one another. The articulated fastening of the tool to the tool carrier may feature a tool receptacle connected in an articulated manner to the tool holder in particular for detachably fastening one or various tools, extension arms, joints, and guides such as for example sliding block guides and/or prestressing elements, for instance springs, for specifying target positions.
According to the invention, a deflection of the tool with respect to the tool holder from a desired position because of a guidance of a component to the tool is detected and a pose of the robot that is guiding this component is changed on the basis of this deflection. In particular, a pose of the robot may be changed on the basis of the detected deflection of the tool in such a way that this deflection is compensated for completely or at least substantially, i.e., the tool is situated at least approximately in its desired position.
A machining position of the component relative to the tool is determined by the linkage of the component to the robot, the linkage being realized for example by a gripper; by the pose of the robot, which is defined by the position of the joints thereof, for instance the angular positions of the pivot joints of a six-axis industrial robot; by the preferably unchanging position of a robot base relative to the tool holder; and by the position of the tool relative to the tool holder that is changeable due to the articulated fastening.
In this case, one or a plurality of machining positions to be approached in succession, for instance for guidance of the component to the tool in such a way that the tool follows a predetermined machining path on the component, for example a grinding pattern, are specified for target values in particular of the component and corresponding poses of the robot are saved, for example taught or programmed offline.
If a component to be machined then deviates from the target values that formed the basis of the specifications, for instance because of manufacturing tolerances, and/or the linkage thereof to the robot deviates from target values, for example due to handling tolerances during gripping by the robot, this produces a deflection of the tool with respect to the tool holder by the robot-guided component. As a consequence, the relative position between the tool and the component changes so that the machining also deviates from specifications in an undesired manner.
Due to the fact that, according to the invention, this deflection is detected and the pose of the robot is changed on the basis of this deflection, it is possible for the deflection to be compensated for, in particular reduced or eliminated so that the component is again in the desired position relative to the tool and is therefore correctly machined by the tool.
In a preferred embodiment, a robot moves a component to be machined, in particular in a translational manner, preferably in a plane perpendicular to at least one axis of rotation of a pivot joint of the articulated fastening of the tool to the tool holder, towards the tool holder in order to compensate for the deflection. Such a translational movement advantageously prevents changes in the orientation of the component with respect to the tool.
The tool is preferably prestressed against a component to be machined. On the one hand, this may cause a yielding of the tool with an increase in this prestress in order to prevent damaging a component in an actual position that deviates from the desired position. In addition, in the case of actual positions that deviate from the desired position in different, in particular opposite, directions, it may advantageously produce a respective deflection, which may be compensated for according to the invention by a corresponding pose change of the robot.
Such a prestress may be realized for example by gravitation, for instance by an articulated suspension in such a way that the tool is raised in the desired position in an articulated manner against the force of gravity, and/or elastically, for example by one or a plurality of springs, which act in one or more, preferably all, degrees of freedom of the articulated fastening of the tool to the tool holder. In addition or as an alternative, a component to be machined may be prestressed actively or in a controlled manner, in particular, in that one or a plurality of forces and/or torques, which act between the component and the tool and/or between the tool and the tool holder, are detected and correspondingly triggered actuators, for example electric motors, are triggered in such a way that the detected actual forces or actual torques approach or reach predetermined force or torques values, which are predetermined for example for the force-closed machining of the component.
In a preferred embodiment a surface condition, in particular a surface structure, of a component to be machined, is detected, in particular by means of an optical detection means, which may preferably have an image processing. A machining process may then be predetermined on the basis of this detected surface condition. For example, a suitable machining path, a suitable machining tool, for instance a grinding granularity, a suitable machining time, a suitable contact force between the component and tool, suitable, for instance raised and/or rough, machining regions and the like may be predetermined. In particular, an actual surface condition may be detected and compared to a target surface condition and a decision may be made whether a machining of this component is carried out at all, because for example the desired target surface condition is already present or is not able to be achieved with the tool, and/or whether a machining of the component, for example a grinding down, is repeated, because the desired target surface condition has not yet been achieved.
Additional features and advantages are yielded from the subordinate claims and the exemplary embodiment. To this end, a single FIGURE in partly schematized form shows the following.